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popcount32.c revision 1.4 
      1 /*	$NetBSD: popcount32.c,v 1.4 2011/08/21 21:25:04 dholland Exp $	*/
      2 /*-
      3  * Copyright (c) 2009 The NetBSD Foundation, Inc.
      4  * All rights reserved.
      5  *
      6  * This code is derived from software contributed to The NetBSD Foundation
      7  * by Joerg Sonnenberger.
      8  *
      9  * Redistribution and use in source and binary forms, with or without
     10  * modification, are permitted provided that the following conditions
     11  * are met:
     12  *
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in
     17  *    the documentation and/or other materials provided with the
     18  *    distribution.
     19  *
     20  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
     23  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
     24  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
     25  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
     26  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     27  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
     28  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
     29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
     30  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     31  * SUCH DAMAGE.
     32  */
     33 
     34 #include <sys/cdefs.h>
     35 __RCSID("$NetBSD: popcount32.c,v 1.4 2011/08/21 21:25:04 dholland Exp $");
     36 
     37 #if !defined(_KERNEL) && !defined(_STANDALONE)
     38 #include <limits.h>
     39 #include <stdint.h>
     40 #include <strings.h>
     41 #else
     42 #include <lib/libkern/libkern.h>
     43 #include <machine/limits.h>
     44 #endif
     45 
     46 /*
     47  * This a hybrid algorithm for bit counting between parallel counting and
     48  * using multiplication.  The idea is to sum up the bits in each Byte, so
     49  * that the final accumulation can be done with a single multiplication.
     50  * If the platform has a slow multiplication instruction, it can be replaced
     51  * by the commented out version below.
     52  */
     53 
     54 unsigned int
     55 popcount32(uint32_t v)
     56 {
     57 	unsigned int c;
     58 
     59 	v = v - ((v >> 1) & 0x55555555U);
     60 	v = (v & 0x33333333U) + ((v >> 2) & 0x33333333U);
     61 	v = (v + (v >> 4)) & 0x0f0f0f0fU;
     62 	c = (v * 0x01010101U) >> 24;
     63 	/*
     64 	 * v = (v >> 16) + v;
     65 	 * v = (v >> 8) + v;
     66 	 * c = v & 255;
     67 	 */
     68 
     69 	return c;
     70 }
     71 
     72 #if UINT_MAX == 0xffffffffU
     73 __strong_alias(popcount, popcount32)
     74 #endif
     75 
     76 #if ULONG_MAX == 0xffffffffU
     77 __strong_alias(popcountl, popcount32)
     78 #endif
     79